The invention relates to a valve arrangement for the pressure regulation of the fuel supply in an internal combustion engine having at least one pressure regulating device and a shutoff device that can be actuated by an electromagnetic drive.
Valve arrangements are known for engines with direct fuel injection. Such engines require injection pressures of approximately 100 to 120 bars. This pressure is produced by high-pressure pumps, which are very sensitive to cavitation and therefore, the fuel that is introduced must be free of vapor bubbles. Under normal engine operation, a positive pressure of approximately 4 bars is sufficient to transport the fuel free of vapor bubbles from a delivery pump to the high-pressure pump. During engine startup, however, the pressure must be increased to approximately 7 bars in order to suppress the formation of vapor bubbles and to reliably establish the injection pressure when the engine is started without utilizing a mechanical high-pressure pump. The required increase in pressure to 7 bars is achieved by a shutoff device that can be activated electromagnetically and by a 4-bar pressure regulation device arranged in front of or behind the shutoff device.
Such a valve arrangement requires a very large structural space and is also very expensive due to the increased expenditure for its assembly.
An object of the present invention is to provide apparatus for overcoming the problems discussed above.
The object is achieved in that a housing is provided with at least one inlet connection and at least one outlet connection, which are in fluid communication by a connection channel, wherein the electromagnetic drive opens or closes the connection channel by means of an armature on a tappet with a closing element, and with at least one pressure spring element which acts directly or indirectly on the closing element in the closing direction.
In this way, a valve arrangement is obtained, which is simple and inexpensive to manufacture and also requires less structural space and a smaller expenditure for assembly. Both the pressure regulation of the fuel supply as well as the shutoff capability is assured by this single component.
In a first embodiment, magnetic force acts on the armature in the closing direction of the closing element, and, in addition, the pressure spring, which is supported on the housing, acts on the armature in the closing direction. This embodiment represents a so-called xe2x80x9ccurrent-free openxe2x80x9d variant. That is, in the absence of electrical current a low pressure level of approximately 4 bars is established by means of the pressure spring. When electrical current is supplied, a magnetic force is applied to the tappet by means of the armature, which raises the pressure to a high-pressure level of approximately 7 bars including the pressure spring.
In a second embodiment, the magnetic force acts on the armature in opposition to the closing direction of the closing element and a first pressure spring acts on the armature in the closing direction, while a second pressure spring acts on the tappet in the closing direction. Both pressure springs are supported by the housing. In this way, a xe2x80x9ccurrent-free closedxe2x80x9d variant of the valve arrangement is produced. The spring forces of the two pressure springs add up to approximately 7 bars when no current is supplied. When current is supplied, the magnetic force acts against the first pressure spring, so that only the second pressure spring with a pressure of approximately 4 bars acts on the tappet in the closing direction.
A particularly simple valve arrangement is then produced if the housing has two inlet connections and two outlet connections. The first inlet connection is connected to the delivery pump and the second inlet connection is connected to the return line from the high-pressure pump. The first outlet connection is connected to the admission line of the high-pressure pump and the second outlet connection is connected to the return line to the fuel tank.
The housing contains an armature core that can be adjustably moved in the housing and which supports the pressure spring such that the pressure applied by the armature can be adjusted in a simple manner. It is also particularly advantageous if the electromagnetic drive has a proportional magnet system, wherein the armature core has an elliptical outer contour. The armature core is thus not exactly round at the magnetic flux transmission site, so that minimum and maximum magnetic forces can be obtained by a 90xc2x0 rotation of the core which in turn makes possible a force adjustment of the electromagnet drive.